1. The Field of the Invention
The present invention relates generally to catalysts for use in reforming hydrocarbons and methods for making and using such catalysts. More particularly, the present invention relates to reforming catalysts comprising supported nanocatalyst particles and a halogen promoter.
2. The Relevant Technology
Naphtha is a volatile, flammable liquid mixture of hydrocarbons distilled from petroleum or other fossil fuel sources. Naphtha can be used as a fuel, a solvent, or in making various chemicals. Typically naphtha is a mixture of hydrocarbons that boil between about 65° C. and about 195° C. and is obtained by processing crude oil and optionally heavy oil fractions.
Naphtha reforming is an important refinery process where naphtha is upgraded into more valuable hydrocarbons having a higher octane rating. In reforming, naphtha is heated and fed into a series of reactors loaded with a solid supported metal catalyst. Typically, the catalyst contains platinum and one or more additional metals, which are supported on alumina. The catalyst also includes a halogen promoter that increases the rate of reforming. The halogen promoter is typically included in an amount that is significantly greater than 1% by weight of the total catalyst.
The main goal of the reforming process is to convert the feed into a liquid product stream with a higher octane number. The octane number is a measure of the performance of the hydrocarbons in a gasoline internal combustion engine. Thus, naphtha reforming converts hydrocarbons streams into a reformate product that is more suitable as a gasoline blending stock. The octane number gain during the reforming process varies depending on, among other factors, the original crude and the reforming conditions. Typical octane value increases are in a range between 30 and 70.
The reforming process involves various parallel and consecutive reactions. The reforming process improves octane by increasing the percentage of branched and/or aromatic compounds. In addition to the production of gasoline blending stocks, reforming is a very significant source of aromatics (e.g., BTX), which are used extensively in the chemical and petrochemical industries (e.g., as solvents or starting materials). The reforming process is also the only refinery operation that yields a net production of hydrogen. Hydrogen is extremely valuable because it finds extensive use elsewhere in a refinery, particularly for the upgrading of low quality hydrocarbon streams.
Among the multiple reactions taking place during the reforming operation, some of them are undesirable, at least to some extent. One of these reactions is hydrocracking, which occurs when a hydrocarbon chain is broken apart into two smaller molecules with a net consumption of hydrogen. Hydrocracking in the reforming process can be undesirable because it consumes valuable hydrogen and can produce smaller hydrocarbon fragments outside the range of liquid reformate product, which is C5 hydrocarbons and heavier (C5+ hydrocarbons). Light gases (C1-C4 hydrocarbons) formed by hydrocracking are not a desired reformate product. Production of C1-C4 hydrocarbons during reforming is considered a loss that reduces the overall yield of the reforming process. While reforming catalysts are essential to improving octane number, reforming catalysts are also known to catalyze hydrocracking.